Refrigeration system having air flow varying means



Nov. 15, 1960 w. L. McGRATH REFRIGERATION SYSTEM HAVING AIR FLOW VARYING MEANS Filed Dec. 19, 1957 FIG.I

DENSE FAN m 2 3 mm mm WM C 7 2 8 2 a T 4 3 3 T 3 1% x w 'lllll EVAPORATOR FAN CW R

INVENT OR.

FIG.2

WILLIAM L-MCGRATH BY S1 ATTORNEY United States Patent REFRIGERATION SYSTEM HAVING AIR FLOW VARYIN G MEANS William L. McGrath, Syracuse, N.Y., assignor to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware Filed Dec. 19, 1957, Ser. No. 703,775

7 Claims. (CI. 62-89) This invention relates to :air conditioning and, more particularly, to a system for limiting the maximum amount of electrical current drawn by an air conditioner.

During operation of an air conditioner, the amount of electrical current drawn by the compressor motor may vary with changes in temperature of the air to be cooled. More specifically, as this temperature increases, the evaporator pressure and hence the density of the gas is increased and the compressor motor may draw more current because of the heavier'load involved. However, it is undesirable for the compressor motor under such pulldown conditions to draw an excessive amount of current which will overload the electrical circuits to which the air conditioner is connected. It is with the limiting of the maximum amount of current which can be drawn by an air conditioner that the present invention is concerned.

It is therefore the object of the present invention to provide a method and apparatus for limiting the maximum amount of current which can be drawn by the compressor motor of an air conditioner in a simple, efficient, and effective manner. Other objects and attendant advantages of the present invention will readily be perceived hereafter.

The apparatus of the present invention consists of a system for limiting the maximum amount of current which can be drawn by an air conditioner comprising a compressor, a condenser, and evaporator, and an expansion member coupled between said evaporator and condenser, a motor coupled to said compressor, a fan for blowing air to be cooled over said evaporator, and means for varying the flow of air produced by said fan in response to changes in load on said compressor.

The method of limiting the maximum amount of current which can be drawn by an air conditioner having a motor driven compressor, condenser, expansion member, an evaporator comprises the steps of blowing air to be cooled over said evaporator, detecting the current drawn by said motor, and reducing the flow of air over said evaporator prior to the exceeding of a predetermined maximum flow of current to said motor. The present invention will be more fully understood when the following portions of the specification are read in conjunction with the accompanying drawings wherein:

Figure 1 is a schematic diagram of an air conditioner embodying the present invention; and

Figure 2 is a schematic wiring diagram of the electrical circuit for an air conditioner showing a modification of the present invention.

In Figure 1 there is shown an air conditioner having a housing 11 which is divided by partition 12 into a condenser chamber 13 and an evaporator chamber 14. A compressor 15, which is positioned in chamber 13, is driven by an electric motor 16. While compressor 15 and motor 16 are depicted as being separate elements, it is to be understood that they may be combined into a hermetic unit, as is well known in the art. A discharge line 17 is coupled to compressor 15 for conducting com- 2,959,929 Patented Nov. 15, 1960 pressed refrigerant to condenser 18. Conduits '19 and 35 having an expansion member 20 'therebetween, which may be a capillary, couples condenser 18 to evaporator 21. A suction line 22 connects evaporator 21 to the suction side of compressor 15 to complete the refrigeration circuit.

A condenser fan 23 is mounted in condenser chamber 13 for directing condenser cooling air over condenser 18 in the well known manner. An evaporator fan 24 is mounted in evaporator chamber 14 for directing air to be cooled over evaporator 21, as is well known in the art. For the sake of clarity, the air inlets and outlets for both the condenser chamber 13 and evaporator chamber 14 have been omitted from the drawing, it being understood that these may be of any type known in the art.

During the operation of the air conditioner, an increase in temperature of the ambient air (which is blown across evaporator 21) will cause a corresponding increase of the temperature of evaporator 21. This increase'in ternperature is accompanied by a corresponding increase in both temperature and pressure of the refrigerant in suction line 22. An increase in the suction pressure in suction line 22 will require greater current to be supplied to motor 16 to efiect compression of the refrigerant. The drawing of additional current by motor 16 is permissible up to a certain predetermined limit. However, when this limit is exceeded, the air conditioner motor 16 will tend to overload the electric circuits in which the air conditioner is placed. It is desirable to maintain the flow of current to motor 16 below this upper limit.

. To achieve the foregoing .desired results, the suction pressure in suction line 22 is reduced by reducing the amount of hot air which is being passed across evapora tor 21 by evaporator fan'24. A thermal bulb 25 may be placed in contact with suction line 22 to sense the temperature of the latter. It will be appreciated that the suction temperature in line 22 is a direct indication of the pressure therein. A capillary 26 couples bulb 25 to bellows 27, which in turn opens or closes switch 28 in response to a predetermined increase or decrease, respectively, of the pressure in suction line 22. More specifically, when bulb 25 senses that a predetermined maximum pressure exists in line 22 which would tend to cause motor 16 to draw excessive current, bellow 27 will open switch 28 to discontinue the flow of current to evaporator fan motor'24, thus stopping it. When fan 24'is stopped, the amount of heat transferred to the refrigerant in evaporator 21 from the hot ambient air is reduced, thus causing a corresponding decrease of the suction pressure in line 22. On the other hand, when the temperature sensed by bulb 25 is reduced below that corresponding to the maximum permissible pressure in suction line 22, bellows 27 will close switch 28 to cause evaporator fan motor 24 to resume its normal operation. It will thus be seen that I have provided a system for controlling the maximum amount of current which can be drawn by the motor of a refrigeration system.

It will be appreciated that bulb 25 may be positioned at various points in the refrigeration circuit where the temperature will reflect .a condition indicative of overloading and that its position is not limited to that shown. For example, bulb 25 may be positioned as at 25 or 25" on conduits 35 or 19, respectively. It may also be positioned as at 25" on discharge line 17. When positioning bulb 25 in the above mentioned alternate positions, it will be appreciated that the switch opening and closing temperatures must be adjusted in accordance with the temperature to be experienced in these alternate positions.

In Figure 2 a modified embodiment of the present invention is shown. Line L has switches 29 and 30 associated therewith. If it is desired to merely operate evaporator fan 24 (Figures 1 and 2) to provide ventilation without cooling, switch 29 is closed while maintaining switch 30 in an open position. If it is desired to operate the air conditioner in the manner discussed above relative to Figure 1, switch 29 is maintained in its open position and switch 30 is closed. 'The closing of switch 30 causes the flow of current through leads 31 and '32. As can readily be seen from the drawing, compressor motor 16 and condenser fan motor 23 will thus be energized. Furthermore, current will flow from line L through switch 30, lead 32, and switch 28 to complete a circuit through evaporator fan motor 24 to energize the latter. A thermal bulb 25, in its preferred location, is placed in contact with line 35 feeding the evaporator to sense the temperature of the latter and thereby give an indication of the pressure therein. When a predetermined pressure is exceeded which corresponds to the maximum, permissible current which may be drawn by compressor motor 16, bellows 27 will open switch 28 and cause it to make contact with terminal 33. In this case there will be flow of current from line L through switch 30, lead 32, switch 28, contact 33, and resistor 34 to complete a circuit through evaporator fan motor 24. However, resistor 34 will cause a predetermined voltage drop which will cause evaporator fan motor to operate at reduced speed, thus causing less of the hot ambient air to be passed across evaporator 21 (Figure 1). The modification of Figure 2 varies from Figure l in that the evaporator fan motor 24 has its speed reduced rather than being stopped completely.

It will thus be seen that I have provided a system for controlling the maximum amount of current which can be drawn by an air conditioner in a simple, eflicient and etfective manner.

While I have disclosed preferred embodiments of the present invention, I desire it to be understood that it is not limited thereto, but may be otherwise embodied within the scope of the following claims.

1 claim:

1. A system for limiting the maximum amount of current which can be drawn by an air conditioner comprising a compressor, a condenser, an evaporator, and an expansion member coupled between said evaporator and condenser, a motor coupled to said compressor, a fan for blowing air to be cooled over said evaporator, a motor driving said fan, and means for varying the flow of air caused by said fan in response to changes in load on said compressor to maintain the current drawn by said compressor motor below a predetermined maximum value, said last mentioned means including a circuit regulating the supply of power to the motor driving said 'fan independently of the supply of power to the motor driving the compressor.

2. A system as set forth in claim 1 wherein said lastmentioned means includes a switch which causes said fan motor to stop when said compressor motor draws a predetermined maximum mount of current.

3. A system for limiting the maximum amount of current drawn by an air-conditioner comprising a compressor, a condenser, an expansion member, and an evaporator forming a refrigeration circuit; a motor for driving said compressor; a fan for blowing air to be cooled over said evaporator; means for detecting the temperature of a predetermined element of the refrigeration circuit; and means coupled to said detecting means for reducing the amount of air blown across said evaporator when a temperature is detected which indicates that said motor is drawing a maximum amount of current.

4. A system as set forth in claim 3 wherein said last-mentioned means reduces said air flow to zero.

5. A system as set forth in claim 3 wherein said temperature detecting means is positioned on a conduit coupling said evaporator and expansion member.

6. A method of limiting the maximum amount of current which can be drawn by an air conditioner having a motor-driven compressor, a condenser, an expansion memher, an evaporator and a fan having a motor controlling operation thereof comprising the steps of blowing air to be cooled over said evaporator, measuring the temperature of the refrigerant in the air conditioner to determine the load on the compressor motor and reducing the flow of air over said evaporator prior to attainment of a pre- 1 determined maximum flow of current to said motor by regulating the supply of power to said fan motor.

7. The invention set forth in claim 1 wherein the last mentioned means is operative to supply an, amount of power to the fan motor to enable it to deliver a flow of air over the evaporator less than its rated capacity.

References Cited in the file of this patent UNITED STATES PATENTS 

